Heart disease, specifically coronary artery disease, is a major cause of death, disability, and healthcare expense. A number of strategies have been developed for treating coronary heart disease, some of which are specifically designed to treat the complications resulting from atherosclerosis and other forms of coronary arterial narrowing.
An important development for treating atherosclerosis and other forms of coronary narrowing is percutaneous transluminal coronary angioplasty, hereinafter referred to as “angioplasty” or “PTCA”. One objective in angioplasty is to enlarge the lumen of the affected coronary artery by radial hydraulic expansion. The procedure may be accomplished by inflating a balloon within the narrowed lumen of the coronary artery. Radial expansion of the coronary artery occurs in several different dimensions, and is related to the nature of the plaque. Soft, fatty plaque deposits are flattened by the balloon, while hardened deposits are cracked and split to enlarge the blood vessel lumen. The wall of the artery itself may also be stretched when the balloon is inflated.
Angioplasty may be performed as follows: A thin walled hollow guiding catheter may be introduced into the body via a relatively large vessel, such as the femoral artery in the groin area or the brachial artery in the arm. Once access to the femoral artery is achieved, a short hollow sheath, or guiding catheter, may be inserted to maintain a passageway during the procedure. The flexible guiding catheter may negotiate an approximately 180 degree turn through the aortic arch to descend into the aortic cusp where entry is gained to either the left or the right coronary artery, as desired.
After the guiding catheter is advanced to the area to be treated by angioplasty, a flexible guidewire may be inserted into the guiding catheter through an expandable balloon and advanced to the area to be treated. The guidewire may be advanced beyond the lesion in preparation for the advancement of a balloon catheter having an expandable balloon portion composed of a resilient material. The balloon catheter may be advanced into position by sliding it along the guide wire. The use of the relatively rigid guide wire is desirable for steerability to advance the catheter through the narrowed lumen of the artery and to direct the balloon, which is typically quite flexible, across the lesion. Radiopaque markers in the balloon segment of the catheter facilitate positioning across the lesion. The balloon catheter may then be inflated with contrast material to permit fluoroscopic viewing during treatment. The balloon is alternately inflated and deflated until the lumen of the artery is satisfactorily enlarged.
While the affected artery generally may be enlarged, in some instances the vessel re-narrows (restenosis) acutely or chronically with time, thereby negating the positive effect of the angioplasty procedure. In the past, vessel restenosis has frequently necessitated repeat PTCA or open heart surgery. While vessel restenosis may not occur in the majority of cases, it occurs frequently enough that such complications comprise a significant percentage of the overall failures of the PTCA procedure, for example, twenty-five to thirty-five percent of such failures.
To lessen the risk of vessel restenosis, various devices have been developed for mechanically maintaining the patency of the affected vessel after completion of the angioplasty procedure. Such mechanical endoprosthetic devices, which are generally referred to as stents, are typically inserted into the vessel in a radially compressed configuration, positioned across the lesion, and then expanded into contact with the vessel wall to maintain an open passageway. Effectively, the stent overcomes the natural tendency of the vessel walls of some patients to re-narrow, thereby maintaining a more normal flow of blood through that vessel than would be possible if the stent were not in place. The stent is typically a cylindrically shaped device formed from wire(s) or a tube and intended to act as a permanent prosthesis. A typical stent may range from about 5 mm to 50 mm in length.
Various types of stents have been proposed, including expandable and self-expanding varieties. Expandable stents are generally conveyed to the area to be treated on balloon catheter assemblies or other expandable devices. For insertion, the stent may be positioned in a compressed configuration along the delivery device, such as a balloon catheter defining a balloon with two folded and wrapped wings, to minimize the stent diameter. After the stent is positioned across the lesion, the stent may be expanded by the delivery device, causing the length of the stent to contract and the diameter to expand. Depending on the materials used in construction of the stent, the stent maintains the new shape either through mechanical force or otherwise.
Self-expanding stents are generally conveyed to the area to be treated on catheter assemblies. Such stents are generally manufactured from resilient materials that can be compressed and then naturally re-expand when deployed. As such, self-expanding stents typically do not require a balloon to provide an expansion force. Some stent designs include a sheath placed over the compressed stent (and balloon assembly) to retain the stent on the balloon and to create an even outer surface on the assembly for negotiation through the narrowed vessels. The sheath may also be used to maintain a self-expanding stent in its compressed configuration. Once the catheter assembly is positioned, the stent may expand as the sheath is slidably retracted.
Prior art stents have included coiled stainless steel springs; helical wound spring coil made from shape memory alloy; expanding metal stents formed in a zig-zag pattern; diamond shaped, rectangular shaped, and other mesh and non-mesh designs. Exemplary stents and catheter assemblies including balloon mounted stents are disclosed in U.S. Pat. No. 6,613,079 issued to Wolinsky, et al.; U.S. Pat. No. 6,589,274 issued to Stiger, et al.; U.S. Pat. No. 6,331,189 issued to Wolinsky, et al.; U.S. Pat. No. 5,833,694 issued to Poncet; and U.S. Pat. No. 6,375,676 issued to Cox.
Some difficulties have been encountered with the deployment of certain self-expanding stents, including difficulties related to placement accuracy. For example, some self-expanding stents can store energy axially from the frictional force generated as the outer restraining sheath is retracted from the expanding stent. This may cause the stent to act somewhat like a spring, storing energy as the frictional force acts on the stent. As the stent expands beyond the end of the sheath, the stored energy may be immediately released, causing the stent to “jump” or slip. This may result in an inaccurate placement of the stent within the body vessel. As such, it would be desirable to provide a strategy for deploying a self-expanding stent that would limit jumping and slippage thereby increasing the accuracy of stent placement.
Accordingly, it would be desirable to provide an intraluminal stent assembly and method of deploying the same that would overcome the aforementioned and other disadvantages.